The present invention pertains to a balancing personal vehicle having a plurality of laterally disposed wheels, wherein improved stability is achieved by non-coaxiality of the wheels.
Personal vehicles may be self-propelled and user-guidable, and, further, may entail stabilization in one or both of the fore-aft or left-right planes, such as when no more than two wheels are in ground contact at a time. Vehicles of this sort may be operated in a mode in which motion of the vehicle, including acceleration (both linear and turning), is controlled partially or entirely by leaning of the vehicle as caused by a subject riding the vehicle. Several such vehicles are described in U.S. Pat. No. 5,971,091, issued Oct. 26, 1999 which is incorporated herein by reference.
Such balancing vehicles may lack static stability. Referring, for example, to FIG. 1a, wherein a prior art personal transporter is shown and designated generally by numeral 18, a subject 10 stands on a support platform 12 and holds a grip 14 on a handle 16 attached to the platform 12, so that the vehicle 18 of this embodiment may be operated in a manner analogous to a scooter. A control loop may be provided so that leaning of the subject results in the application of torque to wheel 20 about axle 22 thereby causing an acceleration of the vehicle. Vehicle 18, however, is statically unstable, and, absent operation of the control loop to maintain dynamic stability, subject 10 will no longer be supported in a standing position and may fall from the platform. Another prior art balancing vehicle is shown in FIG. 1b and designated generally by numeral 24. Personal vehicle 24 shares the characteristics of vehicle 18 of FIG. 1a, namely a support platform 12 for supporting subject 10 and grip 14 on handle 16 attached to platform 12, so that the vehicle 18 of this embodiment may also be operated in a manner analogous to a scooter. Another prior art balancing vehicle is shown in FIG. 1c and designated generally by numeral 42. Personal vehicle 42 includes a seat 44 for the subject 46 on support platform 48. FIG. 2 shows that while vehicle 24 may have clusters 26 each having a plurality of wheels 28, vehicle 24 remains statically unstable and, absent operation of a control loop to maintain dynamic stability, subject 10 will no longer be supported in a standing position and may fall from platform 12. Balancing personal vehicles such as vehicle 18 of FIG. 1a and vehicle 24 of FIG. 1b may have pairs of wheels, such as wheels 30 and 32 shown in FIG. 1b, such that the wheels are substantially laterally disposed. Lateral disposition of wheels, as used in this description and in any appended claims, refers to the disposition of points of contact 34 and 36 of wheels 30 and 32 respectively, with the ground, on a line 38 that lies substantially transverse to the direction 40 of forward motion of the vehicle.
In cases where wheels are longitudinally displaced, such as on a bicycle or motorcycle, the vehicle is typically designed such that, in the absence of steering forces, a wheel will tend to return to the straight wheel travel condition. Such configurations may be said to be self-centering. A prior art vehicle having substantially laterally disposed wheels that are parallel lacks the inherent self-centering mechanism of a balancing vehicle with longitudinally disposed wheels. It is therefore desirable to provide such vehicles with inherent restoring mechanisms.
In accordance with a preferred embodiment of the invention, there is provided a device for transporting a payload over a surface. The direction of motion of the device defines a forward direction. The vehicle has a platform for supporting the payload and a first wheel having a center, with the first wheel coupled to the platform in such a manner as to rotate about a first axis. Additionally, the device has a second wheel having a center, where the second wheel is also coupled to the platform in such a manner as to rotate about a second axis. The platform with the payload and the two wheels constitute an assembly. The center of the second wheel and the center of the first wheel define a lateral axis which is substantially perpendicular to the forward direction, i.e., the wheels are substantially laterally disposed. In accordance with a preferred embodiment of the invention, an angle defined by the first axis with respect to the lateral axis and an angle defined by the second axis with respect to the lateral axis are each non-zero. The device also has a motorized drive arrangement coupled to the ground contacting module for causing locomotion of the assembly and the payload over the surface when the motorized drive is powered, in an operating position that is unstable with respect to tipping when the motorized drive is not powered. In accordance with an alternate embodiment of the invention, the vehicle may have a control loop in which the motorized drive is included for dynamically maintaining stability by operation of the motorized drive arrangement in such a manner that the net torque experienced by the assembly about the point of contact with the surface, taking into account torques caused by gravity and by all other external forces and by the motorized drive, causes a desired acceleration.
In accordance with an alternate embodiment of the present invention, the projections in a lateral plane of the angle defined by the first axis with respect to the lateral axis and the angle defined by the second axis with respect to the lateral axis are both non-zero. Alternately, the projections in a horizontal plane of the same angles may both be non-zero. The device may also have a handle, affixed to the platform, having a grip at approximately waist height of the subject, so that the device may be operated in a manner analogous to a scooter, and may further include a seat coupled to the platform for supporting a human subject.